Method of treating pigments and products produced thereby



Patented on. 21, 1941 METHOD OF TREATING PIGMENTS AND PRODUCTS PRODUCEDTHERE!!! KennethS.

The

1111., amignorto timore, Glidden company, Gevcland, Ohio, a corporationoi 01th No Drawing.

The present invention relates to and particularly relates to pigmentsoi! improved hiding power. More specifically the praent inventionrelates to an improvement on the invention described in Serial No.175,246, filed November 18, 1937.

In said application Serial No. 175,246 there is disclosed a process oftreating pigments whereby their hiding power is greatly improved. Bythis process a pigment is produced the reaction product of a watersoluble silicate and an acid or salt capable of precipitating thesilicate in insoluble form. Among the precipitating agents which may beused are water soluble salts of aluminum, alkaline earth metals,

and acids such as sulfuric acid or other mineral acid.

It has been found preferable in practice to use a salt such as analkaline earth salt to effect the precipitation or the silicate.However,

. the use of salts as precipitating agents results in certaindisadvantages when the treated pigments are used in paints or similardispersions. One of the disadvantages is that the pigments so treatedhave an increased tendency to settling. Another is that in the case of asulfide pigment containing the reaction product of the soluble silicateand a precipitating salt, the pigment is discolored when used withmetallic driers such as lead driers, unless some special treatment isgiven the silicated pigment.

The present invention contemplates a procedure whereby the advantages ofusing salts for the precipitation of the soluble silicate ar obtainedbut without the disadvantages ordinarily resulting from their use.

It has been found that if the soluble silicate is first converted tosilicic acid, and the silicic acid then treated with oxides orhydroxides of alkaline earth metals, zinc, aluminum, or theirequivalents that improved results are obtained According to a preferredmethod a soluble silicate such as sodium silicate is mixed with anaqueous slurry of the pigment being treated. An amount of acid, such assulfuric or hydrochloric, equivalent to the N320 in the sodium silicateis then added with the formation of silicic acid. While the acid iscapable of precipitating the silicate under the proper conditions, asunderstood by those skilled in the art, such precipitation is notnecessary in the present invention and ordinarily will not take place.After the addition of the acid and the formation of silicic acid, anamount of oxide or hydroxide of In April 24, 1939,

Applicaflo Seth! No. 269,786

alent, q ivalent to the NazO or other alkali metal oxide present in theoriginal soluble sillcate is added.

The advantages resulting from the present invention are believed to bedue in part at least to the irecdom oi the treated pigment from salts ofalkaline earth metals, zinc, aluminum, etc. Upon the addition or theacid to the slurry containing the soluble silicate the pigmentdispersion is increased. The alkali metal salt may be removed later, andits removal is much more etc.

sulfide pigments, etc. when they are used in paints containing metallicdriers, such as lead driers. It is believed that the occludedprecipitating salts cause the formation of lead or other coloredsulfides. 1

By employing the procedure of the present invention this occlusion ofprecipitating salt and alkaline earth metals, zinc, aluminum or equivitseifects are overcome.

The invention is applicable to the treatment of pigments generally andis particularly applicable to the treatment of white pigments such aslithopone, TiOz, etc. and inerts such as calcium carbonate, blanc fixe,calcium sulfate, etc. or mixtures thereof. In treating the pigments theamount of silicate may vary, and depends upon various factors.Ordinarily, however, the amount will be from about 0.5% to 10% by weightof the pigment treated. These amounts, however, are not exact, as moreor less may be used. Ordinarily not much less will be used as in mostcases the benefits obtained would not justify the treatment. If desired,more than 10% may be used which may be as much as 20% or more.

The following example is illustrative of the invention:

1000 grams of lithopone are slurried in water, and 204 cc; of a 40' Baumsodium silicate solution containing .1162 gram of NazO per cc. is added.After agitation sumcient hydrochloric acid is added to convert thesilicate into silicic acid. To this mixture is then added grams of Cal).After agitation and the precipitation is complete the pigment isfiltered, washed, dried and ground to produce a finished pigment. Thispigment when used in a paint formula containing a lead drier showed nogreater discoloration than an untreated pigment, whereas a lithoponegiven a silicate treatment employing 08.01: as a precipitating agent.and not given any special treatment to overcome discoloration, showed amarked discoloration in the same paint formula. Also the pigmentproduced did not settle as badly in the paint formulation as did thepigment in which precipitation was carried out by CaClz.

It will be readily appreciated that, if desired, silicic acid may beadded directly to the pigment slurry, and this then converted by theaddition of a suflicient amount of oxide or by. droxide to form theinsoluble silicate with the silicic acid.

Also the insoluble silicate may be separately repared and then mixedwith the base pigment. In such a case the improvement in hiding poweris'not as great as where the precipitation is made with the pigmentpresent, although there is a marked increase in hiding power in eithercase.

Having described my invention what is claimed 1. The process ofimprovingthe hiding power of base pigments which comprises treating silicic acidwith a metallic insolubilizing and precipitating agent therefor selectedfrom the class consisting of oxides and hydroxides of alkaline earthmetals, zinc and aluminum to "convert the silicic acid into thecorresponding insoluble metallic silicate, and mixing the resultinginsoluble silicate with a base pigment.

2. The process of improving. the hiding power of base pigments whichcomprises treating silicic acid with a metallicinsolubilizing andprecipitating agent therefor selected from the class consisting ofoxides and hydroxides of alkaline earth metals, zinc and aluminum toconvert the silicic acid into the corresponding insoluble metallic vsilicate, while in admixture with a base pigment.

3. The process of improving the hiding power of base pigments whichcomprises converting an aqueous metal silicate into silicic acid bymeans of an acid, precipitating the silicic acid with a precipitanttherefor selected from the class consisting of oxides and hydroxides ofalkaline earth metals, zinc and aluminum to convert the silicic acidinto the. corresponding insoluble metallic silicate, while in admixturewith a base pigment.

4. The process of improving the hiding power of base pigments whichcomprises converting an aqueous alkali metal silicate into silicic acid,and precipitating the silicic acid with a precipitant therefor selectedfrom the class consisting of oxides and hydroxides of alkaline earthmetals, zinc and-aluminum to convert the silicic acid into thecorresponding insoluble metallic silicate, allthereafter adding ametallic precipitating agent for the silicic acid selected from theclass con- ,radical of the precipitating agent is an alkaline earthmetal radical.

sisting of oxides and hydroxides of a metal caaqueous-slurry of a basepigment, introducing a soluble silicate into said slurry, adding an acidto convert the soluble silicate into silicic acid and thereafter addinga metallic containing precipitant for the silicic acid, selected fromthe class consisting of oxides and hydroxides of alkaline earth metals,zinc and aluminum to convert the silicic acid into the correspondinginsoluble metallic silicate.

7. The process of claim 6 in which the metal radical of the precipitantis an alkaline earth metal radical.

8. The process of improving the hiding power of a sulfide pigment whichcomprises providing an aqueous solution containing a sulfide pigment,introducing a soluble silicate into said slurry, introducing an acid toconvert the soluble silicate into silicic acid, and thereafter treatingthe silicic acid with alkaline earth oxides and hydroxides.

9. The process of claim 8 in which the sulfide pigment is a zinc sulfidepigment.

10. The process of claim 8 in which the sulfide pigment is lithopone.

11. The process of improving the hiding power of base pigments whichcomprises providing an aqueous slurry of a base pigment, introducing analkali metal silicate into said slurry, adding sumcient acid to convertthe alkali metal silicate into silicicacid, and thereafter adding anamount of an alkaline earth metal oxide stoichiometrically equivalent tothe alkali metal oxide present in the original alkali metal silicate,whereby the silicic acid is converted into an insoluble alkaline earthmetal silicate.

12. The process of improving the hiding power of base pigments whichcomprises providing an aqueous slurry of a base pigment, introducingapproximately 0.5% to 10% by weight of the pigment, of an alkali metalsilicate, adding sufflcient acid to convert the alkali metal silicateinto silicic acid, and thereafter adding an amount of an alkaline earthmetal oxide stoichiometrically equivalent to the alkali metal oxidepresent in the original alkali metal silicate whereby the silicic acidis converted into an insoluble alkaline earth metal silicate.

13. The process of claim 12 in which the pigment comprises a sulfidepigment.

14. The process of claim 12 in which the pigment comprises a zincsulfide pigment.

15. The process of claim 12 in which the pigment comprises lithopone.

16. The process of improving the hiding power of lithopone whichcomprises providing an aqueous slurry of lithopone, introducingapproximately. 0.5% to 10% by weight of the lithopone of sodiumsilicate, adding sufflcient acid to convert the sodium silicate intosilicic acid, and thereafter adding a metal containing precipitant andinsolubilizing agent for the silicic acid selected from the classconsisting of oxides and hydroxides of alkaline earth metals, zinc andaluminum to convert the silicic acid into the corresponding insolublemetallic silicate, the amount of said precipitant beingstoichiometrically equivalent to the Nazo content of the sodiumsilicate.

17. The process of claim 16 in which the metal 18-. The process of claim16 in which the precipitating agent is calcium oxide.

19. The process of claim 11 in which the base pigment comprises titaniumdioxide pigment.

20. The process of claim 11 in which the base pigment comprises amixture of a white pigment selected from the class consisting oflithopone and titanium dioxide, and an inert pigment.

22. The process of improving the hiding power of base pigments whichcomprises treating silicic acid with a metallic precipitating agenttherefor selected from the class consisting of oxides and hydroxides ofa metal capable of forming an insoluble silicate with the siiicic acid,and' mixing the resulting insoluble silicate with the base pigment.

KENNETH S. MOWLDS.

